1. Field of the Invention
The present invention relates to an apparatus and a method for transmitting packets in a wireless network and, more particularly, to an apparatus and method for transmitting packets in a wireless network, which adjusts the number of repetitions of transmission of a packet according to the extent of motion of a mobile terminal.
2. Description of the Related Art
As the use of wireless terminals is becoming more popular due to the development of wireless communication technology, the users of wireless terminals desire to receive stable communication service that enables the uninterrupted transmission and reception of packets even during movements at high speeds, through the wireless terminals. A process in which data is transmitted between mobile terminals based on communication layers is described below with reference to FIG. 1.
FIG. 1 is a diagram showing the flow of data transmission based on the communication layers of a conventional mobile terminal. The communication layers shown in FIG. 1 may be regarded as some of the layers of the Open Systems Interconnection (hereinafter abbreviated as the ‘OSI’) reference model. The OSI reference model is a communication-related standard model established to support uninterrupted connections between different types of computers or networks, and is divided into seven layers. The functions of the respective layers are as follows:
First, layer 1 (the physical layer 40) is responsible for transmitting a bitstream, which is transmitted from an upper layer, through a transmission medium in a specific electrical signal form. Second, layer 2 (the data link layer 30) is responsible not only for transmitting data blocks, which are formed by signal-level data bits passing through the physical layer, but also for handling a synchronization problem, which occurs when identifying the start and end of each data block, and an error problem, which occurs when detecting errors and performing restoration. Third, layer 3 (the network layer 20) constructs an invisible logical link between a transmission side and a reception side, is responsible for dividing data into packets, transmitting the packets, and assembling the packets, and provides a routing function of searching for optimal transmission paths for packets. Fourth, layer 4 (the transport layer 10) is responsible not only for establishing and maintaining connections between users and between computers, but also for providing logical stability and uniform service between transmission and reception systems. Fifth, layer 5 (the session layer) is responsible for establishing sessions, thereby providing a synchronization function to achieve the sequential flow of dialogue without interruption. Sixth, layer 6 (the presentation layer) is a layer handling a method of presenting data, and is responsible for providing a standard interface that enables the presentation of different data. Seventh, layer 7 (the application layer) is the uppermost layer, and functions as a path through which a user's application program accesses a network environment.
The 7 layers of the OSI are divided into two groups. The upper layer group (the transport layer, the session layer, the presentation layer, and the application layer) is used by the user to send and receive messages, while the lower layer group (the physical layer, the data link layer, and the network layer) functions to allow the message to pass through a host.
The flow of data transmission of FIG. 1 is applied to the packet transmission of a wireless terminal data, which is conveyed from the session layer, is divided into segments and is assigned numbers, an error detection code is added thereto, and the flow of communication is controlled. While packets, which are created by layer 7 (the application layer), pass via layer 6 (the presentation layer) and layer 5 (the session layer), and layer 4 (the transport layer). A routing function of searching for an optimal path, through which the packet is transmitted to the destination, is performed while the packet passes through layer 3 (the network layer). Synchronization and error problems are resolved and the packet is transferred to layer 1, that is, the next layer, while the packet passes through layer 2 (the data link layer). The packet will wirelessly arrive at the destination through layer 1 (the physical layer).
In a related art technology for performing the above-described process of transmitting packets, packet loss does not occur frequently in an environment in which motion is low, so the packet transmission rate is high even though the transmission method is used without change. However, in an environment featuring a lot of motion, such as the case in which mobile terminals are used in mobile means moving at high speeds, the packet loss rate increases and, therefore, packets are frequently retransmitted. Accordingly, when packets are frequently retransmitted, problems occur in that the traffic of an overall network increases, so that the packet loss rate increases and, at the same time, the time for which the packet transmission is delayed gradually increases. Accordingly, a scheme for solving the problems is required in the environment featuring a lot of motion.